This project aims to characterize age-related changes in vestibular function, and explore their influence on important gait outcomes that increase fall risk and mortality in older individuals. These aims will be carried out within the Baltimore Longitudinal Study of Aging (BLSA), a rigorous, comprehensive longitudinal study of >1000 individuals age 20-103. Specifically, Aim 1 is to characterize SCC and otolith functional status and age- related variation in the BLSA population, and evaluate these for associations with demographic and comorbid medical factors. We will estimate population means and heterogeneity (variance) in AVOR gain in each SCC plane and cervical and ocular VEMP amplitudes as a function of age. We will evaluate differences in age- related SCC and otolith function by demographic factors (gender, race) and comorbidities (diabetes). In Aim 2, we plan to evaluate longitudinal changes in SCC and otolith function within BLSA participants over 5 years and investigate differences by demographic and comorbid medical factors. In 5 years, ~600 BLSA participants will be evaluated at 3-5 repeated visits. We will estimate mean and heterogeneity in rate of change of AVOR gain in each SCC plane and cervical and ocular VEMP amplitudes as a function of time. We will assess whether rates of change differ by demographic and comorbidity subgroups. In Aim 3, we will investigate the association of SCC and otolith function with age-related gait impairment. We will also evaluate whether a compensatory strategy that improves gaze stabilization modifies the association between SCC function and age-related gait impairment. We will evaluate associations between SCC and otolith function and two important age-related gait impairments - slow gait speed and increased gait variability (e.g. in step length, width, velocity), controlling for potential confounders including ankle proprioception, vision, lower extremity strength and neurocognitive function. A well-characterized compensatory strategy for SCC function loss is the gaze-stabilizing compensatory saccade. Importantly, this saccade can be induced and improved through vestibular rehabilitation. We will evaluate the frequency and timing of this compensatory saccade in the BLSA cohort as a function of age and AVOR gain, and investigate whether early timing of this saccade reduces the impact of low AVOR gain on gait speed and variability. This work represents an interdisciplinary approach to characterize the changes in vestibular physiologic function that occur with aging, and to explore the impact of these changes on clinically-significant outcomes including gait speed and variability and the role of vestibular adaptation in modifying these associations. The proposed work will fill fundamental knowledge gaps about how vestibular physiologic function changes with age. Moreover, findings from this study will inform clinical practice by establishing the range of predicted values for SCC and otolith function by age, by providing expected trajectories for SCC and otolith function according to baseline patient characteristics for individual- level patient counseling, and by identifying specific deficts (e.g. delay of compensatory saccades) that can be targeted clinically to improve functional outcomes and ultimately reduce fall risk in older individuals.